The gibberellic acid signaling repressor RGL2 inhibits Arabidopsis seed germination by stimulating abscisic acid synthesis and ABI5 activity.
Seed germination is antagonistically controlled by the phytohormones gibberellic acid (GA) and abscisic acid (ABA). GA promotes seed germination by enhancing the proteasome-mediated destruction of RGL2 (for RGA-LIKE2), a key DELLA factor repressing germination. By contrast, ABA blocks germination by inducing ABI5 (for ABA-INSENSITIVE5), a basic domain/leucine zipper transcription factor repressing germination. Decreased GA synthesis leads to an increase in endogenous ABA levels through a stabilized RGL2, a process that may involve XERICO, a RING-H2 zinc finger factor promoting ABA synthesis. In turn, increased endogenous ABA synthesis is necessary to elevate not only ABI5 RNA and protein levels but also, critically, those of RGL2. Increased ABI5 protein is ultimately responsible for preventing seed germination when GA levels are reduced. However, overexpression of ABI5 was not sufficient to repress germination, as ABI5 activity requires phosphorylation. The endogenous ABI5 phosphorylation and inhibition of germination could be recapitulated by the addition of a SnRK2 protein kinase to the ABI5 overexpression line. In sleepy1 mutant seeds, RGL2 overaccumulates; germination of these seeds can occur under conditions that produce low ABI5 expression. These data support the notion that ABI5 acts as the final common repressor of germination in response to changes in ABA and GA levels.
Piskurewicz
Urszula
U
Université de Genève, Département de Biologie Végétale, 1211 Geneva 4, Switzerland.
Jikumaru
Yusuke
Y
Kinoshita
Natsuko
N
Nambara
Eiji
E
Kamiya
Yuji
Y
Lopez-Molina
Luis
L
D000040:Abscisic Acid / Q000096:biosynthesis* / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism* / Q000502:physiology*; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D018525:Germination / Q000187:drug effects / Q000502:physiology; D005875:Gibberellins / Q000378:metabolism* / Q000494:pharmacology; D008954:Models, Biological; D010766:Phosphorylation; D030821:Plants, Genetically Modified / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012639:Seeds / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000502:physiology*; D014230:Triazoles / Q000494:pharmacology
C409743:ABI5 protein, Arabidopsis; D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D005875:Gibberellins; C450823:RGL2 protein, Arabidopsis; D012333:RNA, Messenger; C492978:SnRK2 protein, Arabidopsis; D014157:Transcription Factors; D014230:Triazoles; C053370:paclobutrazol; D000040:Abscisic Acid; C007842:gibberellic acid; D017346:Protein Serine-Threonine Kinases